/Engine/Source/Runtime/Engine/Classes/GameFramework/InputDeviceLibrary.h
Get all mapped input devices on this platform regardless of their connection state.
The number of connected input devices
static int32 GetAllInputDevices ( [TArray](API\Runtime\Core\Containers\TArray)< [FInputDeviceId](API\Runtime\Core\Misc\FInputDeviceId) > & OutInputDevices )